Download link only works if user is already authenticated

[carsten-jahn]

Opening a download link directly (e.g. user comes from a different webapp, or link was copied from email etc) results in the tomcat error message: "HTTP Status 401 - This request requires HTTP authentication."

It would be good to redirect the user to the login page in this case, remembering the URL he wanted to open, and then going back to the URL.

Example of download link, as used in irods cloud browser:
https://servername.net:9443/irods-cloud-backend/download?path=/busProd/home/filename.pdf